Messages in this thread | | | Subject | Re: [RFC PATCH v2 08/11] iommu/dma: Support PCI P2PDMA pages in dma-iommu map_sg | From | Robin Murphy <> | Date | Fri, 12 Mar 2021 15:52:57 +0000 |
| |
On 2021-03-11 23:31, Logan Gunthorpe wrote: > When a PCI P2PDMA page is seen, set the IOVA length of the segment > to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), > apply the appropriate bus address to the segment. The IOVA is not > created if the scatterlist only consists of P2PDMA pages.
This misled me at first, but I see the implementation does actually appear to accomodate the case of working ACS where P2P *would* still need to be mapped at the IOMMU.
> Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to > indicate bus address segments. On unmap, P2PDMA segments are skipped > over when determining the start and end IOVA addresses. > > With this change, the flags variable in the dma_map_ops is > set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for > P2PDMA pages. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > drivers/iommu/dma-iommu.c | 63 ++++++++++++++++++++++++++++++++------- > 1 file changed, 53 insertions(+), 10 deletions(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index af765c813cc8..c0821e9051a9 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -20,6 +20,7 @@ > #include <linux/mm.h> > #include <linux/mutex.h> > #include <linux/pci.h> > +#include <linux/pci-p2pdma.h> > #include <linux/swiotlb.h> > #include <linux/scatterlist.h> > #include <linux/vmalloc.h> > @@ -846,7 +847,7 @@ static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle, > * segment's start address to avoid concatenating across one. > */ > static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > - dma_addr_t dma_addr) > + dma_addr_t dma_addr, unsigned long attrs) > { > struct scatterlist *s, *cur = sg; > unsigned long seg_mask = dma_get_seg_boundary(dev); > @@ -864,6 +865,20 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > sg_dma_address(s) = DMA_MAPPING_ERROR; > sg_dma_len(s) = 0; > > + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { > + if (i > 0) > + cur = sg_next(cur); > + > + sg_dma_address(cur) = sg_phys(s) + s->offset -
Are you sure about that? ;)
> + pci_p2pdma_bus_offset(sg_page(s));
Can the bus offset make P2P addresses overlap with regions of mem space that we might use for regular IOVA allocation? That would be very bad...
> + sg_dma_len(cur) = s->length; > + sg_mark_pci_p2pdma(cur); > + > + count++; > + cur_len = 0; > + continue; > + } > + > /* > * Now fill in the real DMA data. If... > * - there is a valid output segment to append to > @@ -960,11 +975,12 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > struct iommu_dma_cookie *cookie = domain->iova_cookie; > struct iova_domain *iovad = &cookie->iovad; > struct scatterlist *s, *prev = NULL; > + struct dev_pagemap *pgmap = NULL; > int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); > dma_addr_t iova; > size_t iova_len = 0; > unsigned long mask = dma_get_seg_boundary(dev); > - int i; > + int i, map = -1, ret = 0; > > if (static_branch_unlikely(&iommu_deferred_attach_enabled) && > iommu_deferred_attach(dev, domain)) > @@ -993,6 +1009,23 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > s_length = iova_align(iovad, s_length + s_iova_off); > s->length = s_length; > > + if (is_pci_p2pdma_page(sg_page(s))) { > + if (sg_page(s)->pgmap != pgmap) { > + pgmap = sg_page(s)->pgmap; > + map = pci_p2pdma_dma_map_type(dev, pgmap); > + } > + > + if (map < 0) {
It rather feels like it should be the job of whoever creates the list in the first place not to put unusable pages in it, especially since the p2pdma_map_type looks to be a fairly coarse-grained and static thing. The DMA API isn't responsible for validating normal memory pages, so what makes P2P special?
> + ret = -EREMOTEIO; > + goto out_restore_sg; > + } > + > + if (map) { > + s->length = 0;
I'm not really thrilled about the idea of passing zero-length segments to iommu_map_sg(). Yes, it happens to trick the concatenation logic in the current implementation into doing what you want, but it feels fragile.
> + continue; > + } > + } > + > /* > * Due to the alignment of our single IOVA allocation, we can > * depend on these assumptions about the segment boundary mask: > @@ -1015,6 +1048,9 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > prev = s; > } > > + if (!iova_len) > + return __finalise_sg(dev, sg, nents, 0, attrs); > + > iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev); > if (!iova) > goto out_restore_sg; > @@ -1026,19 +1062,19 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > if (iommu_map_sg_atomic(domain, iova, sg, nents, prot) < iova_len) > goto out_free_iova; > > - return __finalise_sg(dev, sg, nents, iova); > + return __finalise_sg(dev, sg, nents, iova, attrs); > > out_free_iova: > iommu_dma_free_iova(cookie, iova, iova_len, NULL); > out_restore_sg: > __invalidate_sg(sg, nents); > - return 0; > + return ret; > } > > static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, unsigned long attrs) > { > - dma_addr_t start, end; > + dma_addr_t end, start = DMA_MAPPING_ERROR; > struct scatterlist *tmp; > int i; > > @@ -1054,14 +1090,20 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, > * The scatterlist segments are mapped into a single > * contiguous IOVA allocation, so this is incredibly easy. > */ > - start = sg_dma_address(sg); > - for_each_sg(sg_next(sg), tmp, nents - 1, i) { > + for_each_sg(sg, tmp, nents, i) { > + if (sg_is_pci_p2pdma(tmp))
Since the flag is associated with the DMA address which will no longer be valid, shouldn't it be cleared? The circumstances in which leaving it around could cause a problem are tenuous, but definitely possible.
Robin.
> + continue; > if (sg_dma_len(tmp) == 0) > break; > - sg = tmp; > + > + if (start == DMA_MAPPING_ERROR) > + start = sg_dma_address(tmp); > + > + end = sg_dma_address(tmp) + sg_dma_len(tmp); > } > - end = sg_dma_address(sg) + sg_dma_len(sg); > - __iommu_dma_unmap(dev, start, end - start); > + > + if (start != DMA_MAPPING_ERROR) > + __iommu_dma_unmap(dev, start, end - start); > } > > static dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys, > @@ -1254,6 +1296,7 @@ static unsigned long iommu_dma_get_merge_boundary(struct device *dev) > } > > static const struct dma_map_ops iommu_dma_ops = { > + .flags = DMA_F_PCI_P2PDMA_SUPPORTED, > .alloc = iommu_dma_alloc, > .free = iommu_dma_free, > .alloc_pages = dma_common_alloc_pages, >
| |